package convert;

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public String convert(String s, int numRows){
        if (numRows == 1) return s;

        List<StringBuilder> rows = new ArrayList<StringBuilder>();
        for (int i = 0; i < Math.min(numRows, s.length()); i++){
            rows.add(new StringBuilder());
        }

        int curRow = 0;
        boolean goingDown = false;

        for (char c : s.toCharArray()){
            rows.get(curRow).append(s);
            if (curRow == 0 || curRow == numRows - 1) goingDown = !goingDown;
            curRow += goingDown ? 1 : -1;
        }

        StringBuilder ret = new StringBuilder();
        for (StringBuilder row : rows){
            ret.append(row);
        }
        return ret.toString();
    }
}
